The present invention relates to block polymers comprising methacrylic acid and derivatives of methacrylic acid as well as method for the preparation of such block polymers. In the past, carboxylic acid containing polymers have been typically synthesized by the direct free radical polymerization of various carboxylic acids, as well as ester, or anhydride derivatives thereof with various vinyl comonomers. The corresponding carboxylic salt derivatives or ionomers are typically prepared by partial or complete neutralization of carboxylic acid groups with various basic compounds. Previously known synthetic routes have resulted in the random placement of such acid or ionic groups along polymer backbones. It would be desirable to provide similar polymeric structures having controlled composition and architecture, predictable molecular weights and narrow molecular weight distributions.
It is previously known to use anionic polymerization techniques for the preparation of block polymers having controlled morphology and composition as well as architecture and predictable molecular weights, as well as narrow molecular weight distributions. However, previous attempts to prepare diene-containing block copolymers additionally comprising carboxylic acid or ester moieties have not been successful due to competing reactions involving the carbonyl functionality of such monomers. The incidents of such undesired competing reactions can be severely reduced or even eliminated by the use of protecting groups in the block copolymer chain. For example, 1,1-diphenylethylene polymerized between blocks of ethylenically unsaturated carboxylic acids or esters and diene blocks may be employed to prepare block copolymers in relatively high purity.
Regardless of the method of preparation, such techniques have required the use of reduced temperatures as low as -50.degree. C. or -80.degree. C. due to the instability of the intermediate anionic species. Moreover, 1,1-diphenylethylene is both expensive and of a limited availability, and accordingly, processes involving its use have proven excessively costly.
Group Transfer Polymerization techniques have recently been employed in order to prepare block polymers of polar monomers such as the alkyl methacrylates. Disadvantageously such techniques are not applicable to the preparation of diene containing block polymers.
It would be desirable if there were provided a process for preparing block polymers of diene and carboxylic acids as well as esters or neutral salts thereof which do not require the use of commercially impractical reaction conditions such as reduced temperatures less than 0.degree. C. In addition, it would be desirable to provide a process for the preparation of block polymers comprising dienes and carboxylic acids, as well as esters or neutral salts thereof that does not require the use of expensive reagents such as 1,1-diphenylethylene.